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The blue lines show the cables connecting the GNSS Simulator PRTC, Paragon-neo and Opt 133 converter. The red numbers show the delays associated with each cable segment and the Opt 133 converter. If the PRTC is perfectly calibrated, it will have zero delay (i.e. zero time error) between the incoming GNSS signal and its 1PPS and PTP outputs.
The time-bases of the GNSS simulator and the Paragon-neo must be synchronised to make correct measurements of the PRTC. The PRTC is tested for quality of synchronisation to the GNSS simulator by measuring it’s outputs. In all cases cable propagation delays will add a fixed offset even, this must be compensated for.
Note: the numbers shown in this diagram are chosen to simplify the example. Please use precise cable and Opt 133 delays when calculating compensation numbers for a real test bench.
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The Opt 133 converter can be removed from the 1PPS reference path if Paragon-neo is running R11 and later software. |
Compensation Settings
Paragon-neo requires three compensation figures when testing a PRTC:
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Follow steps 1-5 to compensate the PRTC and Paragon-neo:
The PRTC must be compensated for the RF cable delay from the GNSS simulator - how this is done is device specific - it will typically be entered in nanoseconds of delay, or meters of cable.
Some PRTC’s may allow for output signal compensation, it is recommended that initially the PRTC is tested with zero output signal compensation, and once this has been validated then the operation of any output compensation can be tested.
Paragon-neo 1PPS Reference Cable compensation accounts for the difference between propagation delays of the simulator RF output to PRTC and simulator 1PPS output to the Paragon-neo reference input. In the example above this is 10+18+10 = 38ns.
1PPS measurement cable compensation accounts for the propagation delay of the cable between the PRTC 1PPS output and Paragon-neo measurement port.
Because the PRTC RF input has been compensated (step 1), the Paragon-neo 1PPS Reference Cable compensation number will be a positive number.
If the PRTC has a PTP output, the Paragon-neo DUT Ethernet cable compensation accounts for the propagation delay of the cable between the PRTC PTP output and Paragon-neo measurement port.
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In the example above this is 20ns.
Paragon-neo 1PPS measurement cable compensation accounts for the propagation delay of the cable between the PRTC 1PPS output
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and Paragon-neo measurement
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The difference in the two signal paths must be compensated so that Paragon-neo can accurately measure performance of the PRTC.
In this example the 1PPS reference signal arrives at Paragon-neo before the RF signal arrives at the PRTC. Therefore we need a negative compensation value of 38 - 80 = -42ns to compensate the 1PPS reference signal. Effectively we are delaying the reference 1PPS.
If the propagation delay from the simulator to the PRTC is less that then 1PPS propagation delay from the simulator to Paragon-neo, the compensation would need to be a positive value. Effectively we are advancing the reference 1PPS.
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port. In the example above this is 15ns.
Using the example propagation delays from the pictures above, compensation values are entered into the Paragon-neo GUI through two GUI application panels.
The 1PPS reference compensation
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is compensated in the PTP Emulation > Test Configuration panel.
The Ethernet cable between PRTC and Paragon-neo is also compensated in the Test Configuration panel
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The 1PPS measurement cable
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is compensated in the Delay Compensation field in the 1PPS Time Error Measurement + Time of Day panel.
The 1PPS reference cable compensation can also be entered in this panel, or it will be copied from the PTP Emulation Test Configuration panel.
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The PRTC and Paragon-neo is are now compensated and ready to run Time Error tests on the PRTC.
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Please also refer to the following related FAQ articles for further information: Paragon-neo Option 133: how to measure 1PPS propagation delays |
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